Water ingress into tunnels is a common challenge during construction, particularly in areas with high groundwater levels. Water entering the tunnel can compromise structural integrity, cause delays, and increase costs. Several methods can be used to control water, but pre-excavation grouting is among the most effective. This technique requires thorough ground investigation prior to construction and probing ahead of the tunnel face during excavation to identify water sources. The ground is then treated with an appropriate grouting technique before the excavation of that area. If pre-excavation grouting is not possible or proves unsuccessful, other methods can be employed during construction, depending on the geological and hydrogeological conditions. Post-excavation grouting is a common alternative but can take longer to stop water ingress. It often requires a specially designed grout mix tailored to the ground conditions and water flow. Multiple attempts may be necessary, as water can stop in one location but reappear elsewhere in the tunnel. Dewatering is another method to reduce groundwater levels around the tunnel, effective in certain conditions, particularly soft ground with high groundwater levels. However, this approach may have environmental impacts, which can be mitigated through careful planning and management. Feel free to reach out if you need tunnelling advice for your project during the design, planning or construction. Video credit: Khezr Mohammadamini #tunneleducation #tunnellingpage #tunelfuturistico #tunelizacion #tunelfuturistico #watermanagement #grouting #dewatering #tunnelengineering #artoftunnelling #tunnel #tunnelengineeringisthefuture #tunnel #tunnelling #tunneling #tunel #civilengineering #miningengineering #knowledge #learntunnelling #t #geotechnicalengineering #geologist #undergroundconstruction #undergroundspace #undergroundproject #تونلسازی #tunellingtechnique
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Canada has to watch for this as the ground water elevation is very high.
Tunnel Engineering While pre-construction investigations, including geophysical test methods, can provide only a general idea, they fall short in preventing water ingress, as this depends on specific joint gaps opening up at the tunnel crown or walls. Therefore, there is no substitute for real-time probing, face mapping, and 3D logging and it's interpretation during tunnel excavation to identify where ground treatment is needed. Based on probe hole observations, cement grouting before blasting is a much easier and safer way to prevent water ingress in tunnels than attempting it afterward. It is more advantageous to know specific vulnerable locations rather than having a general understanding.
I have no executive experience in this situation. But with a search I found these items. 1. Grouting 1.1. Cement Grouting: Injecting cement-based materials into the ground can fill voids and reduce permeability. 1.2. Polymer Grouting: This involves using chemical grouts that can expand and seal off water paths more effectively than traditional methods. 2. Dewatering: 2.1. Well Point Systems: These involve a series of small-diameter wells that are pumped to lower the groundwater level. 2.2. Deep Wells: For more significant dewatering needs, deep wells can be drilled and pumped to reduce groundwater pressure. 2.3. Sump Pumps: In smaller excavation sites, sump pumps can be used to remove water that accumulates in the tunnel. 3. Pressure Relief Wells: 3.1. These wells are used to relieve hydrostatic pressure on the tunnel face by allowing water to escape in a controlled manner.
True, pre-grouting is a very efficient way to hinder water ingress in underground spaces and true, water ingress points tend to shift due to grouting. To achieve a dry rock space it usually requires grouting, drainage and shotcrete. By implementing efficient measures under construction phase you reduce costs under construction phase but more importantly you reduce costs under operating phase. The ultimate goal is to provide a sustainable construction that is safe and requires minimal maintenance
It appears to be clear water, and the volume isn’t substantial, likely due to the redistribution of groundwater after the tunnel excavation. Once it’s drained for a while, it should stop. Blocking this type of water isn’t really worth the effort, as it doesn’t significantly affect the structural safety—only making the working conditions worse. This doesn’t seem to be the first occurrence of localised water ingress, as in the distance, you can see previous areas where water was coming through have clearly decreased. The rock conditions here are likely hard rock, possibly granite. Additionally, this kind of localised water ingress is difficult to accurately detect during the survey stage, whether through geophysical methods or drilling, because it’s caused by the groundwater redistribution following the excavation.
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6moTunnel seismic is an effective method for investigating the rock mass condition ahead of the face. In tunneling water ingress is very often controlled by secondary porosity, i.e. fractures opening. Highly fractured zones are easily identified by tunnel seismic. In addition, the evaluation of P and S waves velocity allows for exploring water bearing zones. Reach me out if you want to know more about this method.